Melanophore and fluoroleucophore photo-protect the Arabian killifish, Aphanius dispar, embryo from ultraviolet light

Pigment cells in fish species play crucial roles in forming colour patterns of each species and other physiological characteristics, including photoprotection. Research on animal pigment cells’ photoprotection has primarily concentrated on black pigment cells, known as melanophores. However, the roles of other pigment cells on UV protection remain poorly understood. In addition, UV sensitivity/resistance mechanisms have been studied in a small number of selected model organisms, and difference of UV sensitivity has not been fully investigated in different species. In this study, we use the Arabian killifish embryos as a novel model for studying the mechanisms of UV protection by different pigment cells. This species features highly fluorescent pigment cells called fluoroleucophores and black pigment cells melanophores. The fluorescent pteridine pigments and black melanin pigments are generated by genes gch (GTP cyclohydrolase) and tyr (tyrosinase), respectively. We generated gch-/- and gch-/-tyr-/- double mutant lines using CRISPR/Cas9 genome editing and examined the UV sensitivity of WT and these mutant embryos. Firstly, we have observed that Arabian killifish embryos showed higher UV resistance to the one in zebrafish from which majority of UV toxicity studies was conducted in fish species so far. Secondly, both morphology and gene expression data revealed that the gch-/-tyr-/- double mutant line exhibited the highest UV sensitivity, and the gch-/- line also demonstrated a greater stress response compared to wild type (WT). The study revealed a diversity of UV resistance between fish species and also identified the roles of black and fluorescent pigment cells in providing effective UV protection from the early stages of embryonic development.